In most restaurants in Thailand, you might need to order water to drink since they would not server tap water.

Different from most countries, if you go to restaurant in Thailand, you might need to pay for water.

In most countries, if you order tap water, they would not charge you any coast for it.
In Thailand, however, most restaurants do not serve tap water, but sell bottled water. Mostly, the price of bottled water in restaurant is as same as soda. Drinking tap water is not common in Thailand even though the government put much effort to reach the standards of World Health Organization in 1999.